1. Field of the Invention
This invention relates to irrigation drip emitters, and in particular to in-line drip emitters having a water-retention valve for preventing the draining of water from the associated pipe during periods of low water pressure, and to such emitters providing pressure compensation.
2. Related Art
A drip irrigation system applies water to specific plant or root zone locations in very small controlled quantities. This allows plants to be grown with substantially less water than is used with surface flooding and broadcast drip irrigation methods. It has been found that yet further reduced water use is made possible by employing periodic short time emitter discharges or pulses of water in the range of 0.1 to 0.4 liters per hour. This lowers the water use by an order of magnitude over conventional constant flow drip irrigation methods.
The newer intermittent drip irrigation method reduces soil saturation, watering beyond plant root zones, and on-surface run-off. This results in improved plant physiology, fertilizer distribution, and moisture take up by the plants.
With conventional emitters, water resident in the irrigation tubing after water pressure is turned off bleeds through the emitter, leaving the tubing empty. When irrigation is resumed the tubing must be refilled before all the emitters will emit water. Thus, conventional emitters cannot be used with pulsed irrigation methods because of the extended period of time required to refill the irrigation pipe.
Initially, emitters were developed for mounting on the exterior of an irrigation pipe by inserting an inlet tube through the wall of the pipe. These external or on-line emitters are completely self contained and require individual handling for installation on an irrigation pipe. An external emitter has been developed which prevents the leakage of water from the pipe during periods of low pressure by the use of a membrane that is biased across an inlet opening. Between high-pressure pulses, the water is retained in the irrigation pipe. This allows for the immediate operation of the emitters when water pressure is increased. At relatively high pressures, the membrane is forced away from the inlet, allowing the water to flow into a labyrinth built into the body of the emitter. One such emitter is described as a compensating non-leakage dripper and sold by Netafim Irrigation Equipment & Drip Systems of D. N. Hanegev 4, Israel. This emitter further provides pressure compensation by positioning the membrane between the emitter inlet and outlet, so that at higher pressures the outlet flow is reduced.
A second general type of emitter is the in-line emitter in which the irrigation pipe is made with the emitter enclosed within it. Such emitters typically are formed by a cylindrical or partially cylindrical insert having an outer surface which forms a labyrinth with the pipe interior wall surface. One end of the labyrinth is connected to the pipe interior and the other end is connected to the pipe exterior.
My prior U.S. Pat. No. 5,111,996 discloses an in-line emitter that provides pressure compensation by forcing water through progressively longer portions of the labyrinth. This is provided by serially restricting exit channels in response to increasing pressure. This emitter is effective in providing pressure compensation, but, like a conventional in-line emitter, does not prevent the drainage of the irrigation pipe during periods of low fluid pressure. There thus remains the need for an in-line emitter that retains water at low pressures in the irrigation pipe between high-pressure pulses, and particularly to such an emitter that also provides pressure compensation.